The advantages of centrifugal separation in internal combustion engine oil filtration is well documented in the art, although requirements for modern engines to cater for longer service intervals by ensuring efficient removal of small particles produced throughout the interval by combustion products (sometimes referred to as soot) place conflicting constraints upon such separation apparatus, particularly in respect of requiring very high speeds from a limited source of rotor motive power is, such as the liquid being cleaned.
The difficulties and conflicting requirements for removing such small particulates centrifugally within apparatus economically, physically and functionally suited for a vehicle are set out in U.S. Pat. No. 6,013,700 and in WO-A-02/055207, the latter of which proposes a number of embodiments for a so-called open vessel centrifugal separator rotor that permits not only a long dwell time for oil in the rotor but also operates with a low oil mass in the rotor that permits the separation interface to be further spaced form the rotation axis than previously and faster rotation speed to be achieved with fluid pressure as the motive force. Most significantly, it is capable of being driven at the necessary speed by the oil to be cleaned, as well as, or instead, by liquid or other fluid from that or a separate source. Unlike the more traditional type of centrifugal separator, wherein a rotor comprises a generally cylindrical vessel which is filled with the liquid at elevated pressure by restricting the rate at which the liquid can escape, that is exemplified by the U.S. Pat. No. 6,013,700, the open vessel centrifuge has a liquid-filled separation and containment zone defined adjacent a circumferentially outer wall and extending radially inwardly therefrom only as far as outlet passage means at which liquid can escape at a rate in excess of supply, thereby creating a “shell” of liquid, instead of a container full, that permits faster, less power consuming rotation
In one particular embodiment shown in WO 02/055207 that represents an arrangement suitable for use with an automobile engine, the separation apparatus is mounted to provide a substantially vertical rotation axis for the rotor having such open vessel construction and the liquid to be cleaned is sprayed as a free jet towards inlet means, comprising an annular inlet region extending along and around the rotation axis, separated from the vessel separation zone by a dividing wall having an upwardly divergent collection surface rotating with the vessel, whereby the liquid impinging on the surface is caused by what is conventionally called centrifugal action to collect and spread as a film and migrate longitudinally upwardly and radially outwardly, acquiring by frictional drag a rotational velocity close to, but less than, that of the vessel outer peripheral wall before being freed to transfer from the inlet region to the separation and containment zone. Rotational energy for the whole rotor is derived by causing a jet of liquid or other fluid to impinge on reaction turbine vanes, buckets or like surfaces which react to liquid impingement to drive the rotor, preferably using the liquid to be cleaned and directing the spent liquid onto the inlet means collection surface for conveying to the annular contaminant separation and containment zone defined by the outer peripheral wall of the container vessel as described above.
Although open vessel centrifugal separation apparatus has a more general applicability than in relation to internal combustion engines of vehicles, design of a simple open vessel centrifuge for use with internal combustion engines for automobiles, trucks and like mass produced transport vehicles is constrained by a variety of factors, in particular the cost of manufacture, complexity, size and the like, which effectively limit the source of power and place practical limitations on achieving the high rotational speeds required, such that it is important to ensure that motive power and energy put into rotating the rotor is used most efficiently and not wasted.
It is an object of the present invention to provide liquid driven centrifugal separation apparatus, and open vessel rotor therefor, of greater efficiency than hitherto.
According to a first aspect of the present invention a rotor for centrifugal separation apparatus for separating solid contaminants from a liquid comprises a walled contaminant separation and containment vessel having a longitudinally extending rotation axis, an impervious outer side wall extending about and along the rotation axis spaced radially therefrom and at least one end wall extending from the side wall towards the rotation axis, outlet passage means, leading externally of the vessel disposed radially inwardly with respect to the outer side wall, said walls defining radially inwardly from the outer side wall an annular contaminant separation and containment zone and the outlet passage means defining the radial boundary of the zone, inlet means, arranged to receive liquid to be cleaned and convey it to the contaminant separation and containment zone at a rate less than liquid can be passed by the outlet passage means, mounting means for mounting the rotor for rotation of the vessel about the longitudinal rotation axis, and fluid motor impeller means disposed to receive a jet of drive fluid thereagainst and responsive to drive fluid impingement to rotate the rotor about said longitudinal rotation axis, said inlet means further comprising a liquid inlet region, defined about and along the rotation axis by a divider wall disposed radially between the outlet passage means and the rotation axis, having a liquid inlet end, transfer passage means, spaced from the inlet end, permitting liquid flow between the inlet region and contaminant separation and containment zone, and a collection face of said divider wall facing inwardly towards the rotation axis, characterised in that the inlet means includes collection impeller means comprising at least one collection impeller vane upstanding with respect to the divider wall collection face into the inlet region and extending about the rotation axis and along the divider wall from said inlet end towards said transfer passage means along a helical path, to constrain the liquid to be cleaned injected into the inlet region to follow a helical path in the direction of rotation of the rotor inlet means towards the transfer passage means.
Most conveniently there are a plurality of collection impeller vanes constraining liquid to travel between them.
The motor impeller means may comprises a plurality of helical motor impeller vanes each having surfaces disposed at or adjacent the inlet end of the inlet means, each upstanding with respect to said dividing wall collection face. At least some of the motor impeller vanes may be arranged such that spent drive fluid deflected thereby is directed along the inlet region. Such motor impeller vanes may be axially disposed with respect to the collector impeller vanes such that their function are separated axially or they may overlap axially.
In a preferred form the collection impeller vanes comprises the fluid motor impeller vanes, so that the drive fluid, which may be the contaminated liquid for cleaning, is caused to impinge upon the impeller vanes spread along the inlet region such that energy for rotation is transferred to the rotor through a large part of its travels along the region, not just as a result of impact with a small area of vane near the inlet end.
According to a second aspect of the present invention a centrifugal separation rotor comprising a walled contaminant separation and containment vessel having a longitudinally extending rotation axis, an impervious outer side wall extending about and along the rotation axis spaced radially therefrom and at least one end wall extending from the side wall towards the rotation axis, including outlet passage means, leading externally of the vessel, disposed radially inwardly with respect to the outer side wall, said walls defining radially inwardly from the outer side wall an annular contaminant separation and containment zone and the outlet passage means defining the radial boundary of the zone, inlet means, arranged to receive liquid to be cleaned and convey it to the contaminant separation and containment zone, and fluid motor impeller means to rotate the rotor about said longitudinal rotation axis, also has, between the outer peripheral wall and the outlet passage means of at least one end wall, a discharged liquid guide extending longitudinally with respect to a said end wall operable to inhibit contact between liquid discharged from the rotor vessel by way of the outlet passage means and the external surface of the rotor vessel radially outwardly of the discharged liquid guide.
The rotor may be like that of the preceding two paragraphs insofar as the inlet means further comprises a liquid inlet region, defined about and along the rotation axis by a divider wall disposed radially between the outlet passage means and the rotation axis, and collection impeller means. The discharged liquid guide may comprise a tubular skirt or equivalent surrounding the rotation axis and an annular form of passageway formed by one or more apertures through the end wall, or may comprise one or more tubular ducts each associated with an end wall aperture and extending away from the wall parallel to and or inclined with respect to the rotation axis.
In accordance with a third aspect of the present invention centrifugal separation apparatus comprises a rotor having a liquid separation and containment vessel, a housing including mounting means to support said rotor for rotation about a rotation axis, drainage means to direct liquid exiting the vessel away from the rotor, fluid motor turbine means including drive fluid nozzle means operable to direct a stream of drive fluid to motor impeller vanes of the rotor, and vessel supply means operable to direct liquid to be cleaned to the rotor vessel, and is characterised by the rotor comprising a rotor as defined by any one of the preceding six paragraphs and the rotor vessel supply means comprising liquid nozzle means operable to direct a jet of said liquid to the inlet end of the rotor inlet means.
Preferably the apparatus is arrange to operate with the rotation axis substantially vertical such that the liquid is arrange to move through he inlet region subjected uniformly at all positions about the rotation axis to a relatively strong centrifugal force towards the wall surface a relatively weak gravitational force. Because the gravitational force is so weak in relation to the centrifugal force, to orientation of the inlet and transfer passage ends of the inlet means may be inverted.